1. Field of the Invention
The present invention relates to an optical rotary encoder and a motor control apparatus for detecting and controlling the rotation of a rotating member such as a photoconductor drum of an electrophotographic copying machine or a paper feed roller of a printer.
2. Description of the Related Art
Conventionally, in apparatus in which a rotating member is driven by a motor, a magnetic or an optical rotary encoder is employed to precisely control the rotational speed and the stopping position. In these apparatuses, a rotary scale is attached to the rotating shaft of a motor or to the rotating shaft of a rotating member coupled via a gear or a belt with the rotating shaft of the motor, thereby allowing the rotation condition of the rotary scale to be detected using a sensor. In the case of magnetic rotary encoders, a magnetoresistive device is used as the sensor. On the other hand, a sensor using a light emitting device and a light detecting device is employed for optical rotary encoders.
In applications in which very high precision control is required, as is the case with electrophotographic copying machines in which the rotation of a photoconductor drum is required to be very precisely controlled, it is known to use two sensors in a rotary encoder, as is disclosed, for example, in Japanese Patent Laid-Open No. 7-140844, such that the two sensors are disposed at opposite locations about the rotation center whereby the rotation is controlled on the basis of the mean value of information output from the two sensors. Even when the rotary scale is eccentrically located with respect to the rotation center, the above technique makes it possible to achieve high precision control by compensating for an error due to the eccentricity.
However, in the conventional technique disclosed in Japanese Patent Laid-Open No. 7-140844, although the error can be substantially compensated for when the optical rotary encoder is of the transmissive type, further problems can occur when an optical rotary encoder of the reflective type is used. That is, in the optical rotary encoders of the reflective type, in addition to the eccentricity of the rotary scale, the inclination of the rotary scale with respect to the rotational axis and the vibrating fluctuations of the position of the surface of the slit plate of the rotary scale result in errors which cannot be eliminated by conventional techniques.
In view of the above-described problems, it is an object of the present invention to provide an optical rotary encoder and a motor control apparatus capable of precisely detecting the driving state of a rotating member by compensating for errors due to eccentricity and inclination of an attached scale and an error due to fluctuations of the surface of the scale.
According to an aspect of the present invention, to achieve the above object, there is provided an optical rotary encoder comprising: a scale, in the form of a circular disk, including reflecting and non-reflecting parts disposed alternately along the circumference of the circular disk, and sensors, each including a light emitting part and a light detecting part, for outputting an electrical signal, wherein a light beam is emitted from the light emitting part so as to illuminate the scale with the emitted light beam and a light beam reflected from the scale is incident on the light detecting part, thereby generating an electrical signal corresponding to the amount of light incident upon the light detecting part. In this aspect of the invention, two sensors are disposed on an outer periphery of the scale such that when the orientation of each sensor is defined by the direction from the light emitting part to the light detecting part of each sensor, the two sensors are oriented in a circumferential direction of the scale and such that the locations of the two sensors are substantially point-symmetric about the center of the scale.
According to another aspect of the present invention, there is provided an optical rotary encoder comprising: a scale, in the form of a circular disk, including reflecting and non-reflecting parts disposed alternately along the circumference of the circular disk, and sensors, each including a light emitting part and a light detecting part, for outputting an electrical signal, wherein a light beam is emitted from the light emitting part so as to illuminate the scale with the emitted light beam and a light beam reflected from the scale is incident on the light detecting part, thereby generating an electrical signal corresponding to the amount of light incident upon the light detecting part. In this aspect of the invention, a plurality of sensors is disposed on the outer periphery of the scale such that when the orientation of each sensor is defined by the direction from the light emitting part to the light detecting part of each sensor, the respective sensors are oriented in a circumferential direction of the scale and such that the plurality of sensors is located at substantially equal intervals along the circumference of the scale.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.